1. C++
2. Hand Coding.
3. Threading, everywhere.
4. Use of Modern c++ futures where ever possible, to avoid waiting for things to finish. That requires careful consideration of how things are put together , to avoid waiting for stuff to finish. This takes what would normally be a linear task, from start to end, and breaks it into steps where you often turn things on their head, and do the things that you need last, first. The goal being not to wait for anying. The bottleneck is usually c4d itself now.
5. Since C4D 2024, deformers and generators can be executed asynchronously. A Dev has to implement this carefully, for big benefits. You can not do this with Python. c++ plugins are an order of magnitude faster than any node generators or deformers. when written carefully, a c++ plugin generator or deformer runs rings around anything else. you get to leverage all of the power that c++ gives you.
6. The Evil Clone : C4D Generally expects any object that you are generating from (input), or modifying to be cloned. Thats is how things have always been. How It always was, and still is. Frankly a terrible way to do things. it is what makes c4d inherently slow. Cloning and changing is the bottleneck.  Sometimes there are better ways to do that.  You can find a good example of alternative methods in practice, with the DEM Earth Contour object. it generates splines, from a polygon object. It is crazy fast, because it does not clone the input object it generates from. It works the opposite way to a standard generator. It goes under or after the input. No cloning, nothing is duplicated and nothing then needs to be released. It goes straight to spline generation, which makes it crazy fast.